Delivery devices for administering a beneficial agent to a biological, fluid environment of use are known to the prior art. See, for example, U.S. Pat. Nos. 5,137,727; 5,174,999; and 5,238,687.
These devices comprise a housing including fluid-impermeable first wall section and a fluid permeable second wall section. A beneficial agent is enclosed within the first wall section. An expandable driving member is enclosed within the second wall section. A slidable piston separates the beneficial agent from the expandable driving member. An exit passageway is formed in the fluid impermeable wall section. As fluid is imbibed through the semipermeable wall section, the driving member expands within the housing, pushing the slidable piston which forces the beneficial agent through the exit passageway.
The delivery devices described in the above patents operate successfully for their intended use and they can deliver many beneficial agents for their intended effects. Now, it has been observed that their use can be limited because difficulties associated with these delivery devices which include beneficial agents that are sensitive to biological fluids and to fluids containing biological gases; uneven delivery of those beneficial agents from the device and difficulties associated with shortening the start-up time for delivering the beneficial agents from the device.
Implanted devices are continually exposed to biological fluids naturally present in the body. Many beneficial agents, including proteins, peptides, and hormones, may be degraded (e.g., hydrolyzed) or diluted by fluids that enter the implanted device during operation thereof. The fluids may contact the agents by entering through the exit passageway, through the wall joints, or around the slidable piston. In addition, the delivery of beneficial agents from these devices may be uneven. Bubbles may impede passage of the agents through the exit passageways. Pressure may be created by differential expansion between the agent formulation and the materials used to construct the device altering the actual agent delivery rate. Furthermore, the disclosed devices may be unable to provide the desired delivery rates and start-up times.
Thus, there is a need for a delivery system for administering a drug or other beneficial agent that is sensitive to aqueous biological fluids at a controlled rate and for protecting the beneficial agent, and which delivery device possesses the ability to continually deliver the protected beneficial agent in effective amounts, over the desired time, particularly in the fields of human and veterinary medicine (eg, in the breeding and management of farm animals).